Note: Descriptions are shown in the official language in which they were submitted.
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Method and apparatus for axially shaping a tube
The invention relates to a method in accordance with the generic term of claim
1
and an apparatus in accordance with the generic term of claim 12 for the axial
shaping of a tube with the aid of a mandrel, which is guided in the tube, and
an
annular die, which is guided on the outside of the tube.
Prior art
The axial shaping of tubes has been established in the metal industry for
decades.
Indents, flares and special contours, such as tooth ings, squares, etc., are
among
the standard applications. Axial shaping means resource efficiency, an
uninterrupted fiber flow, strain hardening of the tube material and good
surface
quality of the shaped regions. The main field of application for the axial
shaping of
tubes is the production of components for the automotive industry and general
mechanical engineering. Axial shaping can also be used to easily produce
lightweight components in particular; this is why axial shaping is also coming
into
play in current topics such as electromobility and the reduction of CO2
emissions.
Shaping is performed with the aid of a mandrel guided in the tube and an
annular
_
die guided on the outside of the tube, the inside diameter of which is, as a
rule,
smaller than the original outside diameter of the tube. The energy for the
shaping
work is provided by both hydraulic and electromechanical systems.
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A sub-case of general tube shaping is the so-called "axial stretching" or
"stretch
forming," as the case may be, of the tube; see for example the technical book
entitled "Fertigungstechnik von Fritz Schulze, Springer Vieweg Verlag, 10th
edition, page 445, Chapter 5.4.3. During axial stretching, the annular gap
between
the die and the mandrel is typically set to a distance that is smaller than
the
original wall thickness of the tube to be shaped. The tool pair of die and
mandrel is
then guided in the axial direction along the tube to be shaped, reducing the
wall
thickness of the tube accordingly.
Each of the printed publications DE 30 16 135 Al, DE 30 21 481 Al, DE 35 06
220 Al and US 6 779 375 B1 discloses the method steps in accordance with the
generic term of claim I.
An example of tube shaping can also be found disclosed, for example, in
international patent application WO 2006/053590 Al. A method for producing
hollow shafts with end portions of greater wall thickness, and with at least
one
intermediate portion of reduced wall thickness from a tube with originally
constant
wall thickness, is described therein. Production is carried out by initially
inserting a
mandrel with a diameter graduated along its length into the tube to be shaped
and
then moving a ring die from the side with the tapered diameter of the mandrel
in
the longitudinal direction over the tube with the internal mandrel. Thereby,
the
outer diameter of the original tube is initially reduced, and at the same time
the
displaced material of the tube is forced into the annular gap between the
annular
die and the stepped mandrel. Due to the gradation of the mandrel, this creates
stepped undercuts inside the tube. The inner contour of the tube created in
this
manner corresponds in a complementary manner to the profile of the stepped
_
mandrel. Over the graduated regions of the mandrel, this creates undercuts
inside
the tube, which typically have a greater wall thickness than the original
tube. If the
annular gap between the die and the portion of the mandrel with the largest
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outside diameter is smaller than the original wall thickness of the mandrel,
the
stretching of the tube occurs in this region, reducing the original wall
thickness to a
smaller wall thickness.
A disadvantage of the procedure known from WO 2006 / 053590 Al is that the
formation of undercuts inside the tube is only possible with individual
discrete wall
thicknesses, to the extent that this is specified by the gradations in the
outer
diameter of the mandrel. In addition, the formation of a plurality of
undercuts on
the outside in the longitudinal direction of the tube is not possible.
Tubes with undercuts on their inside and outside are also known from the
company Schmittergroup; see the following link on the Internet:
https://www.schmittergroup.de/de/produkte/details/rohre-mit-variabler-
wanddicke.html .
Based on this prior art, the invention is based on the object of further
developing a
known method and a known apparatus for shaping a tube in such a way that it is
possible to form undercuts both on the inside and on the outside of the tube
with a
wall thickness that can be variably set within limits.
Such object is achieved by the method claimed in patent claim I. This is
characterized in that, when an end position of the die is reached with the
mandrel
leading, the following steps are carried out:
Reversing the direction of movement of the die and mandrel from the pushing
direction to an opposite pulling direction; First setting step: Moving the die
and
mandrel in relation to one another to a first preset annular-gap setting; and
first
_
shaping step: Moving the die and mandrel in the pulling direction over a first
partial
portion of the free tube portion, while maintaining the first preset annular-
gap
setting, for shaping the tube.
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The first setting step and any subsequent setting steps allow the die and the
mandrel to be moved in relation to one another and thus the annular gap
between
the die and the mandrel to be variably set to any desired dimension -
preferably
limited to the original outside diameter as a maximum. Due to the presence of
conical transition portions with both the annular die and the mandrel,
undercuts
are possible in the shaping region of the tube, particularly within the
original tube
wall thickness, because of the variable setting of the annular gap. Depending
on
whether the conical transition portions taper or flare towards the free end of
the
tube, the undercuts are possible on the inside and/or outside of the tube. The
formation of undercuts on the inside of the tube and on the outside of the
tube can
be realized in one operation on one and the same tube on different
longitudinal
portions in each case. As a sub-case of this, a thick-thin tube with a
constant inner
bore can also be realized, with which only local undercuts are formed on the
outside. Alternatively, thick-thin tubes can be formed with a constant outside
diameter, but with undercuts inside the tube with different wall thicknesses
on
request.
The said undercuts are formed by moving a tool pair of die and mandrel, preset
with respect to the annular gap, over a partial portion of the free tube
portion. In
accordance with the invention, the die and mandrel are moved in the pulling
direction to form the undercuts, that is, when the tool pair is moved towards
a
shaping device, in which the die and mandrel are displaceably mounted and
controlled. In particular, "pulling direction" also means a direction in which
the tube
to be shaped is subjected to tensile load. In contrast to moving the die and
mandrel in a pushing direction, which is opposite to the pulling direction,
there is
no risk of the tube being deformed in an undesirable way, in particular
compressed
_
or bent, when the die pair is moved in the pulling direction.
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Advantageously, the claimed method enables the creation of completely
different
geometries on the tubes with regard to diameter tolerances and work
thicknesses
by means of program-controlled shaping sequences, without the geometries of
the
tools, that is, the die and the mandrel, having to change during the shaping
process. The method in accordance with the invention allows the use of simple
(pre-) tubes, which did not already have to be pre-shaped in separate method
steps, and thus better value-added potential in component production. The use
of
forward and backward movements of the die - mandrel tool pair for shaping the
tube signifies resource efficiency. The method in accordance with the
invention
allows a targeted reduction of the wall thickness of the tubes in limited
local tube
portions according to a previously made design layout. The local reduction of
the
wall thickness of a tube may be desired, for example, to introduce a
predetermined
breaking point. Another advantage is the possibility of using inexpensive pre-
tubes
in accordance with the German Industry Standard DIN EN 10305-3 instead of the
previously required tubes of a more expensive quality according to the
standard
DIN EN 10305-2.
Definitions:
The term "free tube portion" means: unclamped tube portion.
The terms "push" or "pushing direction" mean a direction away from a shaping
device, from which the die and mandrel are moved, and towards a clamping
device. In particular, the pushing direction means a direction in which the
tube to
be shaped is subjected to pressure.
The term "pulling direction" means a direction opposite to the pushing
direction.
_
With the pulling direction, the tube to be shaped is always subjected to
tensile
load. There is no risk of compressing or bending the tube. However, when
shaping
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in the pulling direction, there is a risk of fracture or cracking of the tube
to be
shaped if the tensile load becomes too great.
The term "synchronous" in the present description means the movement of die
and mandrel at the same speed in the same axial direction. Synchronous travel
always takes place with a fixed annular gap. Changing the size of the annular
gap
always requires relative movement of the die and mandrel at different speeds,
which precludes the synchronous movement of the die and mandrel.
The term "vertical" refers to the y-direction of the coordinate system, as
shown in
Figure 1.
The term "negative annular gap" means that annular gap that is spanned by the
conical transition portions of the die and mandrel that taper towards the free
end of
the tube or towards the mandrel bar or towards the shaping device, as the case
may be, in the figures. Independently of this, the conical transition flanks
of the die
and mandrel can be designed to converge, be parallel or diverge in relation to
one
another. Thereby, the conical transition portions can overlap or oppose each
other,
as the case may be, at least a short distance in the vertical direction. In
the
figures, the mandrel is then offset to the left with respect to the die. In
other words,
the negative annular gap - viewed in the pulling direction - is located on the
rear
side of the die. Machining the tube with a negative annular gap results in the
formation of an undercut on the outside of the tube.
The term "minimum annular gap" means an annular gap with a minimum vertical
distance between the die and the mandrel. It is formed in particular between
the
narrowest point of the annular die and an opposite, usually cylindrical
(transition)
_
portion of the mandrel. As a rule, the die - mandrel tool pair is selected
prior to the
beginning of tube shaping, such that the minimum annular gap dimension
corresponds to a later desired minimum wall thickness of the tube to be
shaped.
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The minimum wall thickness is usually selected to be less than or equal to the
original wall thickness of the tube. It can be realized later by axial
stretching of the
tube.
The term "positive annular gap" means an annular gap that is expanded by the
conical transition portions of the die and mandrel flaring in the figures
towards the
free end of the tube or towards the mandrel bar or towards the shaping device,
as
the case may be. Independently of this, the conical transition flanks of the
die and
mandrel can be designed to converge, be parallel or diverge in relation to one
another. Thereby, the conical transition portions can face each other in the
vertical
direction, at least to some extent. In the figures, the mandrel is then offset
to the
right with respect to the center of the die. In other words, the positive
annular gap -
viewed in the pulling direction - is located on the front side of the die.
Machining
the tube with a positive annular gap results in the formation of an undercut
on the
inside of the tube.
In accordance with a first exemplary embodiment of the invention, after the
first
shaping step, the sequence of steps, setting step and subsequent shaping step,
can be repeated as often as desired, in which case the annular gap can be re-
set
at each further setting step. Such repeatability of the steps allows multiple
undercuts to be shaped on the inside and outside of the tube, distributed over
the
longitudinal direction of the free tube portion to be machined.
The provision of a cylindrical portion in the longitudinal direction of the
mandrel
makes it possible to set the minimum annular gap between the die and the
mandrel, if the specified cylindrical portion with the maximum outer diameter
of the
mandrel faces the narrowest point of the annular die. If the die and the
mandrel
_
are moved in this relative position to each other in the longitudinal
direction of the
tube, the axial stretching of the tube takes place if the set minimum annular
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distance between the die and the mandrel is smaller than the upstream wall
thickness of the tube in the pulling direction.
Alternatively, the annular gap between the mandrel and die can be set
negatively
or positively to form an undercut on the inside or outside of the tube.
Depending on the current situation and the previous shaping of the tube, the
relative movement of the die and mandrel can take place in different ways
within
the framework of the setting steps. Specifically, with the first claimed
setting step,
with which the direction of movement of the die and mandrel is reversed, it is
useful for the die to be stopped for a brief period of time and then for only
the
mandrel to be moved relative to the die, in order to set the desired annular
gap. In
other situations, it may be useful to continue moving the die continuously in
the
pulling direction and to change the setting of the annular gap by moving the
mandrel relative to the moving die. In other situations, it may be useful to
move the
die temporarily a short distance in the opposite direction to the pulling
direction,
that is, in the pushing direction, while the mandrel remains stationary, in
order to
adjust the annular gap as desired.
Both for shaping the undercuts in the inner and outer regions of the tube and
for
carrying out the aforementioned axial stretching of the tube, the die and the
mandrel typically move synchronously with each other while maintaining a
previously undertaken setting of the annular gap. The die and mandrel are
moved
synchronously until a desired length portion of the tube to be shaped, in
which the
respective undercuts or stretchings are to be made, has been run.
It is particularly advantageous if the method in accordance with the invention
is
_
used to alternately carry out the formation of undercuts and the stretching of
the
tube in the longitudinal direction of the tube on the tube portion to be
shaped.
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The above-mentioned object of the invention is further achieved by an
apparatus
for carrying out the method in accordance with the invention in accordance
with
patent claim 12. The advantages of this apparatus correspond to the advantages
mentioned above with reference to the claimed method.
The control device required for carrying out the method in accordance with the
invention for the individual control of the die and mandrel is designed as an
electronic control, in particular for the individual setting of the annular
gap for
realizing the undercuts and the stretching. However, for setting the minimum
annular gap, as required in particular for the axial stretching of the tube,
the control
device can also be designed in the form of a mechanical forced coupling.
Compared to an electronic control system, the formation of a mechanical forced
coupling is particularly simple and robust. Finally, it is advantageous if the
mandrel
is designed to be profiled - in particular in the longitudinal direction. With
the aid of
a profiled formation of the mandrel, for example if the mandrel has a
gearwheel-
shaped cross-section, longitudinal grooves can be drawn in or formed, as the
case
may be, on the inside of the wall of the tube with such mandrel.
The description is accompanied by 18 figures, where
Figure 1 shows the apparatus for carrying out the method in
accordance with
the invention in an initial position;
Figure 2 shows the mandrel and die in an initial position for
reducing the
outside diameter of the tube;
Figure 3 shows the die and mandrel in an end position after
reduction of the
_
outside diameter of the tube;
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Figure 4 shows the beginning of a first stretching of the tube
beginning from
an end position;
Figure 5 shows the end of stretching the tube over a first partial
portion of the
free end of the tube;
Figure 6 shows the setting of a negative annular gap at the
beginning of the
formation of an undercut on the outside of the tube;
Figure 7 shows the completion of the formation of the undercut on
the outside
and the beginning of a second stretching process;
Figure 8 shows the end of the second stretching process;
Figure 9 shows the change of the ring gap setting at the end of the
second
stretching;
Figure 10 shows the setting of the annular gap with positive increase
to initiate
the formation of an undercut inside the tube;
Figure 11 shows the end of the formation of the undercut inside the
tube,
Figure 12 shows another change in the setting of the annular gap to
initiate a
third axial stretching operation;
Figure 13 shows the end of the entire tube shaping with the die
removed from
the tube and the mandrel largely extracted;
_
Figure 14 shows the shaped tube after the shaping steps described
above
have been carried out;
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Figure 15 shows the formation of longitudinal grooves on the inside
of the tube
by using a mandrel with a gearwheel-shaped cross-section;
Figure 16 shows the shaping device in accordance with the invention
with the
formation of a forced coupling or forced guidance, as the case may
be, for the die at the beginning of a reduction of the outer diameter;
Figure 17 shows the shaping device moved to an end position in the
pushing
direction with a left-side stop on a clamping device; and
Figure 18 shows the shaping device after a reversal of its direction
of
movement in the pulling direction with the die now stopping on the
left side.
The invention is described in detail below with reference to the above figures
in the
form of exemplary embodiments. In all figures, the same technical elements are
designated with the same reference signs.
Figure 1 shows the apparatus in accordance with the invention. It includes a
clamping device 140 for clamping a tube 200 to be shaped, such that a free
portion 210, that is, a portion of the tube 200 that is not a clamped portion,
remains
for shaping. At the free end of the tube 200, a shaping device 150 can be
seen, in
which an annular die 120 and a mandrel 110 arranged coaxially thereto are
displaceably mounted. In the exemplary embodiment shown herein, the die 120
_
includes two conical transition portions on the inside, a first transition
portion 120-1
of which tapers towards the free end of the tube 200 and a second transition
portion 120-11 of which flares towards the free end of the tube 200. The
mandrel
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110 has a first conical transition portion 110-1 on its outside, which tapers
towards
the free end of the tube 200 and towards the shaping device 150, and a
transition
portion 110-11 that flares towards the free end of the tube 200 and towards
the
shaping device 150. A cylindrical transition portion 110-111 with a constant
maximum outer diameter is formed in between. The pairing of annular die 120
and
mandrel 110 is selected such that the minimum distance between the die at its
narrowest point and the cylindrical portion 110-111 of mandrel 110 having
maximum
outside diameter is less than or equal to the original wall thickness of the
tube 200.
In order to carry out the method in accordance with the invention, it is not
absolutely necessary that each of the die 120 and the mandrel 110 has two
conical transition portions. To realize undercuts 220, 240 on the outside of
the
tube 200, only the conical transition portions on the die 120 and mandrel 110,
which taper towards the free end of the tube 215, are required. To form
undercuts
220, 240 only inside the tube 200, only the transition portions on the die 120
and
mandrel 110, which flare towards the free end 215 of the tube and towards the
shaping device 150, are required. If only a stretching of the tube 200 is
desired,
only the presence of the cylindrical portion 110-111 at the mandrel 110 with a
maximum outside diameter without conical transition portions is required.
Depending on the desired shaping of the tube 200, the die 120 and the mandrel
110 must be selected in each case with the correspondingly necessary
transition
portions and minimum annular gap.
A control device 152 is allocated to the shaping device 150 for moving the die
120
and the mandrel 110 independently of each other along the free portion 110 of
the
tube 200 in a pushing direction S and a pulling direction Z. When the die 120
is
moved in the pushing direction, the tube 200 is subjected to compression and
_
there is a risk of bending and compression of the tube 200. When the die 120
and
mandrel 110 are moved in the pulling direction, there is a risk of the tube
200
tearing, in particular if the annular gap is set too narrow.
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Figure 1 shows the initial position of mandrel 110 and die 120 for carrying
out the
method in accordance with the invention. The mandrel 110 and die 120 are
located at the free end of the tube 200 and aligned coaxially with it. The
mandrel
110 has already moved a short distance into the free end of the clamped tube
200.
Figure 2 shows the beginning of a desired reduction of the outer diameter of
the
tube 200 by pushing the annular die 120 in the pushing direction S towards the
clamping device 140. Given that the smallest clear inside diameter Dm of the
die
120 is smaller than the outside diameter DR of the tube 200, the desired
reduction
of the outside diameter occurs when the die 120 is moved in the pushing
direction.
Thereby, the wall of the tube 200 slides along the transition portion 120-1 of
the die
120. The mandrel 110 thereby precedes the die 120 in the pushing direction S;
it is
not involved in the shaping process itself in that its surface does not
contribute to
the shaping, that is, specifically to the reduction of the outer diameter.
During this
shaping process, it serves at most to guide and support the tube 200 against
bending.
In contrast to the subsequent shaping step, with which the die 120 and the
mandrel 110 are moved in the pulling direction, the annular gap between the
die
120 and the mandrel 110 is not important when the outer diameter is reduced by
moving the die 120 in the pushing direction; its size is irrelevant; in
particular, the
mandrel 110 can advance so far in front of the die 120 that a conical
transition
portion of the mandrel 110 facing the die 120 has no influence on the wall of
the
tube 200 if the latter is reduced by the movement of the die 120.
In accordance with Figure 3, the reduction of the outer diameter DR of the
tube 200
_
occurs over an essential part of the free portion 210, specifically in this
case until
the die 120 abuts the clamping device 140. Of course, the end of the reduced
tube
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portion defined in this way is merely exemplary; in fact, the reduction of the
tube
200 can end even before it reaches the clamping device 140.
In Figure 3, it can be clearly seen that the material displaced during the
reduction
of the outer diameter results in an increase in the wall thickness of the tube
200 in
the region of the reduced outer diameter.
In order to reverse this increase in wall thickness, at least in a first
partial portion
T1 of the free end of the tube 200, the die 120 and the mandrel 110 are moved
to
their minimum ring spacing dmin in a first setting step, in accordance with
Figure 4.
For this purpose, the direction of movement of the mandrel 110 is reversed
from
the pushing direction S to the opposite pulling direction Z, and the mandrel
110 is
moved towards the die 120. To set the minimum annular gap dmin, as already
mentioned, the mandrel 110 is moved relative to the die 120 such that the
cylindrical portion 110-III of the mandrel faces the location of the annular
die with
the smallest annular diameter.
Such setting of the minimum annular gap by changing the position of the die
120
and the mandrel 110 in relation to one another can be made, on the one hand,
electronically or, on the other hand, as shown in Figures 16 to 18, with the
aid of a
mechanical forced coupling of the die 120 and the mandrel 110 within the
shaping
device 150. A traversing carriage 153 is provided within the shaping device
150 for
the axial movement of the die 120 in the pushing and pulling directions. A
mandrel
bar 113 is arranged coaxially with the traversing carriage 153 for the axial
movement of the mandrel 110 in the pushing and pulling direction. With
electronic
control, the traversing carriage 153 with the die 120 and the mandrel bar 113
with
the mandrel 110 - electronically controlled - are moved independently of each
other in the axial direction.
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In the case of forced coupling, the die 120 is mounted in or on, as the case
may
be, the traversing carriage 153 so as to be displaceable with an axial
clearance x
in the axial direction. Their movement is limited by two stops 150-1 and 150-
11 in
the axial direction. In the initial position shown in Figure 16 at the
beginning of a
movement in the pushing direction to reduce the outer diameter, the die 120
strikes the right-side stop 150-1 within a traversing carriage 153. From this
initial
situation, the traversing carriage 153 is moved together with the die 120 and
synchronously with the mandrel 110 in the pushing direction S towards the
clamping device 140. Figure 17 shows the stop of the traversing carriage 153
at
the clamping device 140. During the specified movement in the pushing
direction
S, the die 120 always strikes the right-side stop 150-1. In the embodiment of
the
shaping device with the specified forced coupling, the traversing carriage 153
of
the shaping device 150 is mechanically coupled to the mandrel 110 or to the
mandrel bar 113, as the case may be. This means that a movement of the
carriage 153 in the axial direction is carried out by the mandrel 110 with the
mandrel bar 113 in the same way.
When the stop position of the carriage 153 on the clamping device 140 shown in
Figure 17 is reached, the die 120 remains at its right-side stop position 150-
1, as
already mentioned. At the same time, the mandrel 110 is offset or advanced, as
the case may be, to the left relative to the die 120 due to the forced
coupling with
the traversing carriage 153 - as was also the case during the entire previous
pushing movement. In order to achieve a change in the setting of the annular
gap
to the minimum annular gap dmin in this situation, the direction of movement
of the
carriage 153 - and coupled with this also the direction of movement of the
mandrel
110 - is reversed from the pushing direction S to the pulling direction Z, and
the
traversing carriage 153 initially moves together with the mandrel 110 a short
distance in the axial direction according to the axial clearance x. Until
then, the
position of the die 120 remains unchanged, but the mandrel 110 is moved
towards
the die 120 in the pulling direction. This changes the annular gap between the
die
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120 and the mandrel 110. In accordance with the invention, the clearance x is
dimensioned such that, in accordance with Figure 18, the cylindrical portion
110-III
of the mandrel 110 moves exactly below the smallest clear diameter of the die
120. In this way, in accordance with Figure 18, the minimum annular gap dmin
is
preset for the subsequent shaping step of axial stretching.
The minimum ring spacing dmin can be less than or equal to the original wall
thickness of the tube 200. In any case, in accordance with Figure 4, it is
smaller
than the increased wall thickness of the tube 200 due to the reduction of the
outer
diameter. In this respect, Figure 4 shows the beginning of a subsequent first
shaping step, with which the direction of movement of the die 120 is also
reversed
from the pushing direction S to the pulling direction Z. Within the framework
of
such first shaping step, the die 120 and the mandrel 110 are then moved in the
pulling direction Z while maintaining the preset minimum ring distance dmin.
Thereby, the specified axial stretching of the tube takes place for the
purpose of
reducing the increased wall thickness to the size of the annular gap dmin.
Preferably, the die 120 and the mandrel 110 move synchronously. However, the
synchronous method is not absolutely necessary during axial stretching; the
only
prerequisite would be that, when the die 120 and the mandrel 110 move in
relation
to one another, the region of the smallest inner diameter of the die 120 moves
in
the region of the cylindrical portion of the mandrel 110, such that the
minimum
annular gap dmin is maintained constant during axial stretching.
Figure 5 shows the end of axial stretching over the first partial portion T1
of the
free tube portion.
At this point, in accordance with Fig. 6, after the first shaping step, a
second
setting step is performed, with which the annular gap between the die 120 and
the
mandrel is newly set. Specifically, the annular gap is set negatively here,
that is,
the setting is made such that the annular gap is spanned by the conical
transition
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portions 110-1 of the mandrel 110 and 120-1 of the die 120, which taper or
converge, as the case may be, towards the free end 215 of the tube 200. Viewed
in the vertical direction, such transition portions face each other in
regions. The
newly set annular gap is located on the rear side of die 120 as viewed in the
pulling direction Z. The change in the position of die 120 and mandrel 110 in
relation to one another takes place in the region of a tube portion TE2
following the
first partial portion T1.
The tool pair of die 120 and mandrel 110 is then moved further in the pulling
direction Z with this new negative annular-gap setting, and an undercut 220 is
formed in the second shaping portion T2 on the outside of the previously
thickness-reduced tube.
Figure 7 shows the end of the second shaping portion T2.
At the end of the desired length T2, the die 120 and the mandrel 110 are again
set
to the minimum ring distance dmin, that is, moved in relation to one another.
This is
done via a further setting portion TE3; see Fig. 7.
In accordance with Figure 8, the die 120 and mandrel 110 are then moved over a
further partial portion T3 of the free tube portion 210 while maintaining the
minimum annular gap dmin. In such third partial portion T3, the tube 200 is
again
axially stretched to reduce the wall thickness to the minimum annular gap
dmin.
In accordance with Figures 9 and 10, the annular-gap setting is then changed
again; this time to a positive annular gap. With such positive annular gap,
the
annular gap is spanned by the conical transition portions 120-11 and 110-11 of
the
die 120 and mandrel 120, which are flared towards the free end of the tube
215.
With such positive annular-gap setting, such conical transition portions with
flaring
towards the tube end are generally opposite each other as seen in the vertical
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direction, at least in sections. The positive annular gap is formed on the
front side
of the die 120, as viewed in the pulling direction. In accordance with Figure
9, the
positive annular-gap setting is realized by the die 120 temporarily reversing
its
direction of movement in the pushing direction at the end of the third partial
portion
T3 and in this way changing its relative position to the stationary mandrel
110, in
such a way that the specified positive annular gap is set. However, this way
of
changing the setting of the annular gap is only exemplary; of course, the
relative
position at the end of T3 could also be achieved by moving the mandrel 110
further in the pulling direction relative to the die 120, which is stationary,
for
example, albeit with the use of force. Of course, the movement of both the die
120
and the mandrel 110 in relation to one another would also be conceivable.
Moving the die 120 and mandrel 110 while maintaining the now set positive
annular gap results in the formation of an undercut 240 on the inside of the
tube
200, as shown in Figure 11. The formation of the undercut 220, 240 extends
over
a partial portion T4 of any desired length. At the end of the fourth partial
region T4,
the ring gap can again be changed, for example again to the minimum ring gap
dmin. Then, after a further setting portion TE5, a fifth partial portion T5
results again
with the axially stretched tube; see Figures 12 and 13.
Figure 14 shows the finished tube 200 after all the individual steps described
above have been carried out.
It is important to mention that the sequence of steps explained here and the
final
result shown in Figure 14 are merely exemplary with regard to the machining
steps
performed. Thus, after the one-time reduction of the outer diameter of the
tube
200, any sequences of axial stretching, formation of undercuts 220, 240 on the
outside of the tube 200 and formation of undercuts on the inside of the tube
200
are possible. In particular, the sequence of portions with axial stretching
and the
formation of undercuts 220, 240 proposed here is not mandatory. Rather, formed
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undercuts 220, 240 on the outside may also be immediately followed by formed
undercuts 220, 240 on the inside of the tube 200 in the pulling direction; and
vice
versa. The partial portions over which the shaping of the tube 200 takes place
in
each case can in principle be of any length; they are limited only by the
length of
the free portion 210 of the tube 200. Thus, axial stretching, the formation of
an
undercut 220, 240 on the outside or the formation of an undercut 220, 240 on
the
inside of the tube 200 can also take place continuously over the entire free
portion
210.
The wall thickness of the tube 200 in the region of an undercut 220, 240
depends
on the actual set positive or negative annular distance, that is, the actual
distance
between the conical transition portions. Due to the electronic setting of the
die 120
and the mandrel 110 in relation to one another, this distance and thus the
wall
thickness in the region of an undercut 220, 240 can be set highly precisely to
any
desired dimension.
Figure 15 shows an example of the shaped tube 200 when a profiled mandrel 110
is used, specifically when a mandrel 110 with a gearwheel-shaped cross-section
is
used. In this way, it is then possible to realize, for example, an internal
toothings
260 of the tube 200 over a long length in the case of very thin-walled tubes
200.
The production of external toothings is also possible when using appropriately
profiled ring dies. The forces required, in particular tensile forces, to
realize such
toothings are significantly lower than using dies 120 and mandrels 110 without
any
corresponding toothing.
List of reference signs
_
110 Mandrel
110-1 Axially extending conical transition portion of the
mandrel, which is
tapered towards the free end of the tube;
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110-11 Axially extending conical transition portion of the mandrel, which
is
flared towards the free tube end;
113 Mandrel bar
120 Die
120-1 Axially extending conical transition portion of the die, which is
tapered towards the free end of the tube
120-11 Axially extending conical transition portion of the die, which is
flared
towards the free tube end
130 Annular gap
140 Clamping device
150 Shaping device
150-1 Right-side stop for die
150-11 Left-side stop for die
152 Control device
153 Traversing carriage
200 Tube
210 Free portion of the tube
215 Free end of the tube
220 Undercuts on the outside of the tube
240 Undercuts on the inside of the tube
260 Internal toothing of the tube
S Pushing direction
Z Pulling direction
E End position
T1, T2, T3 Partial portions of the free tube portion with shaping
TE1, TE2, TE3 Transition portions of the free tube portion for changing the
annular-
gap setting
DR Original outer diameter of the tube
Dm Minimum clear inner diameter of the annular die
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dmin Minimum annular gap
_
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